Transcutaneous electrical nerve stimulation (TENS) is a non-invasive technique in which a low-voltage electrical current is delivered through wires from a small power unit to electrodes located on the skin. Electrodes are temporarily attached with paste in various patterns, depending on the specific condition and treatment goals. TENS is often used to treat pain, as an alternative or addition to pain medications. Therapy sessions may last from minutes to hours.

TENS devices can be set in a wide range of frequencies and intensities, depending on patient preferences, desired sensations, and treatment goals. "Conventional TENS" involves the delivery of high or low frequency electrical current to affected areas. In "acupuncture-like TENS," lower frequencies are used at specific "acupuncture points" or trigger points. TENS may also be applied to locations on the ear ("auricular points"). Epidural stimulation and percutaneous electrical nerve stimulation (PENS), which are not included in this review, are invasive procedures that require penetration of the skin, implantation, or minor surgery.

The practice of using electricity for pain control can be traced to 2500 BC and the Egyptian Fifth Dynasty, in which stone carvings depict an electric fish being used to treat pain. During the Socratic era, electrogenic torpedo fish (Scribonius longus) were used to treat arthritis and headache. In the Middle Ages, electrostatic generators were used, and the discovery of the electric battery in the 19th century led to further experimentation.

The use of electrical stimuli for pain relief was popularized in the 19th century and became widespread in the 1960s and 1970s using battery power.

TENS has been hypothesized to improve pain in multiple ways. Theories include effects on sensory nerves, interference with sensory-discriminative pathways, stimulation of release of natural chemicals that affect the way pain is perceived and transmitted (for example, encephalins and endorphins), or through increased blood flow in treated areas such as the skin or heart. Recent data suggest pain relief from low and high frequency TENS is mediated by the release of mu or delta-opioids, respectively, in the central nervous system, and reductions in substance P. However, none of these mechanisms has been clearly established in scientific research, and the basis of activity of TENS remains controversial. Theories used traditionally to explain acupuncture have also been offered, citing effects on flow of vital energy. It is also sometimes suggested that TENS may affect the cardiovascular system, increasing heart rate and reducing blood pressure.

Many studies of TENS compare the technique to "placebo" techniques in which a TENS-like control box and electrodes may be used without delivering electric current to the patient. However, patients can often tell if no current is delivered, which lessens the quality of these studies. Much of the research on TENS is not well designed or reported.

These uses have been tested in humans or animals. Safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider.

GRADE *

Several small randomized controlled trials in adults and children report pain reduction or reduced need for pain medications during dental procedures with the use of various TENS techniques. These studies provide promising preliminary evidence but do not include clear descriptions of design or results. Therefore, better research is necessary before a strong recommendation can be made.

B

Multiple randomized controlled trials have examined the effects of TENS in patients with osteoarthritis of the knee. Overall, the results suggest improvements in knee stiffness and pain, although it is not clear that walking distance or swelling are improved. The available studies have been small without clear descriptions of design or results. Therefore, better research is necessary before a strong recommendation can be made.

B

Auricular TENS is sometimes used in Europe to reduce the need for anesthesia during surgical procedures. There is not enough reliable evidence to draw a firm conclusion in this area.

C

Preliminary research suggests that TENS may benefit some symptoms of Alzheimer's disease, including mood, memory, and cycles of daily rest and activity. Additional human study is necessary before a firm conclusion can be drawn.

C

Several small, brief studies report benefits of TENS on angina pectoris pain. However, most studies were conducted during the late 1980s and early 1990s, and were not well designed or reported. New drugs for heart disease have been developed since these studies were conducted, and people with heart disease or chest pain are advised to seek immediate medical attention from a licensed physician.

C

There is not enough reliable evidence to draw a firm conclusion in this area.

C

The effects of TENS or acupuncture-like TENS on low back pain remain controversial, and multiple controlled trials have been published in this area. Studies have not been consistent in the type of TENS techniques used (location, intensity, frequency, duration) or in definitions of back pain, and most trials have not been well designed or reported. Published meta-analyses have grouped some of these studies together to try to determine whether this technique is effective, but have also yielded inconsistent results, with some authors reporting overall benefits, and others finding no clear advantage over placebo. Better-designed research is needed before a firm conclusion can be reached.

C

There is not enough reliable evidence to draw a firm conclusion in this area.

C

There is not enough reliable evidence to draw a firm conclusion in this area.

C

The effect of TENS on chronic pain of various causes and locations remains controversial, and multiple controlled trials have been published in this area. Although numerous studies report benefits, studies have overall been small, poorly designed, and without clear descriptions of results. Better-designed research is needed before a firm conclusion can be reached.

C

TENS has been examined for the treatment of dysmenorrhea in several small studies. Research in this area suggests that the use of TENS may reduce short-term discomfort and need for pain medications. However, the available trials do not clearly describe study designs or results. Most outcomes are not measured using validated scales. Overall, blinding, randomization, dropouts, and statistical analysis are not well described. Sample sizes are small. Therefore, the research in this area remains indeterminate.

C

Preliminary controlled trials suggest that TENS may have some benefits in patients with migraine or chronic headache. Additional well-designed research is necessary before a firm conclusion can be reached in this area.

C

There is not enough reliable evidence to draw a firm conclusion in this area.

C

The effect of TENS on labor pain remains controversial, and multiple controlled trials have been published in this area. Although some research reports small benefits, including reduced need for pain medications, studies have overall been small, poorly designed, and without clear descriptions of results. Better-designed research is needed before a firm conclusion can be reached. It is not clear if passage of electricity using TENS has harmful effects on the fetus.

C

TENS has been tested for its effects on pain control during lithotripsy (a technique used to break up gallstones). Currently, there is not enough reliable evidence to draw a firm conclusion in this area.

C

Several studies report benefits of TENS in patients with chronic facial pain of various causes. However, these trials have been small without clear descriptions of design or results. Therefore, additional research is needed before a firm conclusion can be drawn in this area.

C

There is preliminary data that high frequency/high intensity TENS may benefit myofascial pain. However, currently there is insufficient evidence from well-designed controlled trials to support this use.

C

There is not enough reliable evidence to draw a firm conclusion in this area.

C

There is not enough reliable evidence to draw a firm conclusion in this area.

C

There is not enough reliable evidence to draw a firm conclusion in this area.

C

Several case reports and a small number of controlled trials report improvements in pain symptoms in people with peripheral neuropathy or nerve damage. However, these studies have not been well designed or reported, and additional research is needed before a firm conclusion can be drawn about effectiveness.

C

There is not enough reliable evidence to draw a firm conclusion in this area. Promising preliminary research requires confirmation with better quality studies.

C

TENS has been used in post-herpetic neuralgia, however there is insufficient evidence from controlled clinical trials upon which to base recommendations.

C

There is conflicting evidence from clinical trials on the effectiveness of TENS in post-operative ileus. Well-designed, large studies are needed before a recommendation can be made.

C

There is not enough reliable scientific evidence to firmly conclude if TENS is beneficial in patients with pain after surgery.

C

There are multiple controlled studies of TENS for pain following various types of surgery, including abdominal surgery, heart surgery, lung surgery, gynecologic surgery, and orthopedic surgery.

Research is inconsistent, with a variety of TENS techniques, patient types, and study designs used. Overall, the quality of available research is poor. Although some studies do report improvements in pain and reduced need for pain medications, a well-designed review in 1996 concluded that there is no clear evidence of benefit. Better quality research is necessary in this area before a strong conclusion can be reached.

C

Studies of TENS in post-stroke rehabilitation report inconsistent findings, and benefits have not consistently been demonstrated. Additional research is necessary before a clear conclusion can be reached.

C

Preliminary studies of TENS in rheumatoid arthritis report improvements in joint function and pain. However, most research is not well designed or reported, and better studies are necessary before a clear conclusion can be reached.

C

TENS has been tested for its effects on blood flow to skin flaps used in plastic surgery procedures such as breast reconstruction. Currently, there is not enough reliable evidence to draw a firm conclusion in this area.

C

TENS has been evaluated in patients with diabetic foot ulcers and chronic ulcers of other causes. There is not enough reliable evidence to draw a firm conclusion in this area.

C

There have been limited non-controlled trials of TENS in spinal cord injury. Well-designed controlled trials are required to recommend for or against the use of TENS for this indication.

C

There is insufficient reliable evidence to recommend for or against the use of TENS in temporomandibular joint pain.

C

There is not enough reliable evidence to draw a firm conclusion in this area.

C

* Key to grades

A: Strong scientific evidence for this useB: Good scientific evidence for this useC: Unclear scientific evidence for this useD: Fair scientific evidence for this use (it may not work)F: Strong scientific evidence against this use (it likley does not work)

Tradition / Theory
The below uses are based on tradition, scientific theories, or limited research. They often have not been thoroughly tested in humans, and safety and effectiveness have not always been proven. Some of these conditions are potentially serious, and should be evaluated by a qualified healthcare provider. There may be other proposed uses that are not listed below.

Safety
Many complementary techniques are practiced by healthcare professionals with formal training, in accordance with the standards of national organizations. However, this is not universally the case, and adverse effects are possible. Due to limited research, in some cases only limited safety information is available.

TENS is generally reported as well tolerated. Skin irritation and redness are the most common adverse reactions, occurring in up to one-third of patients. Hives, welts, or contact dermatitis/allergic skin reactions may occur with the use of electrodes and electrode paste. Electrical burns may occur with excess use or improper technique. Due to the risk of burns, TENS should be used cautiously in people with decreased sensation, such as with neuropathy.

TENS should not be used in patients with implantable devices such as defibrillators, pacemakers, intravenous infusion pumps, or hepatic artery infusion pumps. Electrical shocks or device malfunction may occur.

There are isolated case reports of lung atelectasis and edema, paresthesias, pain, and increased hair growth with the use of TENS. Seizures have been reported, and TENS should be used cautiously in people with seizure disorder. Unpleasant sensations at and away from the site of TENS, headache, muscle aches, nausea, agitation, and dizziness have also been reported. It is also sometimes suggested that TENS may affect the cardiovascular system, increasing heart rate and reducing blood pressure.

TENS cannot be recommended during pregnancy due to insufficient evidence, and due to a theoretical risk of harm to the fetus. Fetal heart rate may be elevated. Although multiple trials of TENS for pain relief during childbirth have been published, interference with fetal heart monitoring equipment may occur, and this technique should not be used unless under the strict supervision of an experienced licensed healthcare practitioner. Safety of TENS is not established in children.

The information in this monograph is intended for informational purposes only, and is meant to help users better understand health concerns. Information is based on review of scientific research data, historical practice patterns, and clinical experience. This information should not be interpreted as specific medical advice. Users should consult with a qualified healthcare provider for specific questions regarding therapies, diagnosis and/or health conditions, prior to making therapeutic decisions.